Well here's some news out of left field. It appears that Sony and nVidia have been jointly developing the PS3 GPU:

TOKYO and SANTA CLARA, CA. DECEMBER 7, 2004 Sony Computer Entertainment Inc. (SCEI) and NVIDIA Corporation (Nasdaq: NVDA) today announced that the companies have been collaborating on bringing advanced graphics technology and computer entertainment technology to SCEI highly anticipated next-generation computer entertainment system. Both companies are jointly developing a custom graphics processing unit (GPU) incorporating NVIDIA next-generation GeForce and SCEI system solutions for next-generation computer entertainment systems featuring the Cell processor.